This invention relates to apparatus and method for inspecting elastic products such as condoms and, in particular, to electro-optical means for detecting the presence of holes and related defects in these products and for determining the thickness of the products.
In the discussion to follow condoms are used to illustrate problems encountered and solved by the invention and its application. However, it should be understood that condoms are used by way of example and that any number of related products (e.g., surgical gloves) made of similar substances to the condoms may be tested electro-optically in accordance with the invention.
It is essential to determine the integrity of condoms because condoms are used to prevent the transmission of body fluids during sexual intercourse and other activity. Also, the use of condoms is intended to prevent the transmission of the AIDS virus and other bio-hazards by blocking physical contact with blood and other body fluids. This fact places special importance on the integrity of the barrier afforded by condoms against microscopic viruses and bacteria. It is therefore extremely important to ensure that there are no holes and like defects in the condoms.
The problem of determining the size and location of holes may be best understood by noting that a latex condom is made by dipping a mold (mandrel) into liquid latex and then passing the latex-coated mold through a curing oven. The condom is then removed from the mold and coated with a powder to prevent stickiness of the surface. A known method for "electrically" testing the integrity of a condom includes mounting the condom onto a metal mandrel and dipping the mandrel covered by the condom into an electrically conducting liquid (bath). Electrical apparatus measures the current flow between the metal mandrel and the electrically conductive liquid. If the current flow is above a preselected threshold current setting, the condom is assumed to have one or more pinholes which allow the electrically conducting liquid to reach the metal electrode. The condom is then identified as being defective and is rejected. After the electrical test, each condom passing the electric conductivity test is removed from the metal mandrel and packaged.
The presently known electrical conducting liquid test which is equivalent to a resistance measurement is a go-no-go test that does not provide information on the size, number or location of the holes. The effectiveness of the electrical resistance measurement is questionable because of the uncertainty of the minimum size pinhole that can be detected with such instrumentation and the effect of air bubbles and lubricating powder that may block the flow of conductive liquid into the pinhole. In addition, this test also does not give information regarding the thickness of the condom being tested.
Furthermore, the conductive liquid ("bath") test requires the immersion of a condom into a liquid whose conductivity has to be controlled and which may affect the condom material. Subsequently, the condom has to be "dried". Thus, the "bath" test requires substantial handling and care. Where it is desirable and/or required that condoms (or like substances) undergo a 100% in-line inspection, a more effective testing of the condoms is desired.
It is an object of the invention to enable optical inspection of condoms which can be incorporated in a production line.
It is a further object of the invention to have inspection equipment which can, in addition to detecting defective condoms, provide data on the size and location of defects, and on the thickness of the condom and on variations in the thickness of the condom. Such equipment may be used to aid in correcting the manufacturing process and thereby reduce the number of defective condoms manufactured.